The invention relates to a filter assembly. Particularly, but not exclusively, the invention relates to a filter assembly designed and adapted for use in a vacuum cleaner. More particularly, the invention relates to a filter assembly for use in a vacuum cleaner and which is used to protect the motor and fan unit.
Motor filter assemblies for removing dust remaining entrained in the air stream of a vacuum cleaner or other dust retaining appliances are common. Such filter assemblies generally comprise at least one filter located in a filter housing. Commonly, two or three filters are arranged in series in the filter assembly to maximise the amount of dust captured by the filter assembly. A known type of filter comprises a first foam filter which is located directly in the air stream and has a large dust retaining capacity. An electrostatic or HEPA grade filter, which is capable of trapping very small dust particles, in particular particles of less than one micron, is then provided downstream of the foam filter to retain any dust which escapes from the foam filter. In such a known arrangement, little or no dust is able to exit the filter assembly. It is known to provide a foam filter which is removable from the filter assembly for cleaning. WO 99/12635 discloses an air filter for respiratory apparatus comprising a series of filters; foam, electrostatic and HEPA. The filters are located in two separate housings, a first housing having a washable foam pre-filter and a second housing having both electrostatic and HEPA grade filters. The foam pre-filter retains the major portion of the entrained dust and is removable for cleaning. However, this arrangement is limited in that the electrostatic or HEPA grade filters, which retain dust which may escape the foam pre-filter, cannot be removed for cleaning. Therefore, the filters in the second housing will require to be replaced at frequent intervals.
It is an object of the present invention to provide a filter assembly suitable for use in a vacuum cleaner or other appliance which has a large capacity for retaining dust and wherein the filter components of the filter assembly do not require to be replaced at frequent intervals. It is a further object of the present invention to provide a filter assembly which retains the ability to contain dust under large back pressures. Further, it is an object of the present invention to provide a filter assembly for use in a vacuum cleaner or other appliance in which the motor is reliably protected and in which the maintenance costs of the vacuum cleaner or other appliance are reduced.
The invention provides a filter assembly for use in a vacuum cleaner having a first filter portion comprising a foam filter, and a second filter portion located downstream of the first filter portion and consisting of a HEPA grade filter medium, the first and second filter portions being held directly adjacent one another by means of a filter housing, the foam filter of the first filter portion being, in use, exposed directly to a dust-laden airflow, and the first filter portion being removable from the filter assembly, characterised in that the first filter portion further comprises an electrostatic filter located on the side of the foam filter facing the second filter portion. In such an arrangement, any dust which may escape from the foam filter is trapped by the electrostatic filter before it reaches the HEPA filter. Little or no dust will be deposited on the HEPA filter under normal use conditions. This prolongs the life of the HEPA filter since it is effective to separate dirt and dust only under extreme conditions, which are infrequent. Further, the foam filter and the electrostatic filter can be removed for cleaning in a single operation.
Preferably, the electrostatic filter is bonded to the foam filter. Bonding the electrostatic filter to the foam filter ensures that there can be no misplacement or misalignment of the electrostatic filter. If the electrostatic filter were inaccurately positioned, dust that might otherwise have been trapped in the electrostatic filter will pass to the HEPA filter. If this were to happen, the HEPA filter would need to be replaced more frequently. Bonding the electrostatic filter to the foam filter ensures that this does not happen. Further, bonding the electrostatic filter to the foam filter provides a filter core that can be easily removed from the filter assembly for cleaning. Alternatively, the electrostatic filter may be removably attached to the foam filter.
Preferably, the first filter portion is washable. The first filter portion will generally retain most of the dust or dirt entrained in the airflow. When the filter portion becomes less efficient than is desired due to excess loading, the user is able merely to wash the filter portion and, after drying, the first filter portion can be returned to the filter assembly for further use. The maintenance costs of the appliance are thus reduced.
Preferably, the second filter portion is washable. This means that the entire filter assembly can be cleaned by washing, which in turn means that replacement filters are not required. When the filter assembly becomes less efficient than is desirable due to excess loading, the user is able to wash both the first and second filter portions and, after drying, the filter assembly can be returned to the vacuum cleaner (or other appliance) for further use. Advantageously, maintenance costs of the appliance are thus reduced.
Preferably, the first and second filter portions are at least partially enclosed by means of the filter housing. Preferably, at least one of the filter portions is bonded to the filter housing. More preferably, the second filter portion is bonded to the filter housing. This ensures that the second filter portion cannot be misplaced or misaligned when the first filter portion is removed for washing.
Preferably, the first filter portion has a tab or gripping portion located on a surface thereof remote from the second filter portion to facilitate removal of the first filter portion from the filter housing. Advantageously, this provides a means for removing the first filter portion from the filter housing, when it needs to be cleaned, without the user having to directly handle it.
Further advantageous features are set out in the subsidiary claims.